Hydraulic operating arrangement for clutches and the like

ABSTRACT

The friction clutch between the prime mover and the change-speed transmission in the power train of a motor vehicle is actuatable by a slave cylinder cooperating with a master cylinder wherein the piston is movable by a clutch pedal or by an electric actuator. The casing of the slave cylinder is made, at least in part, of a plastic material and defines a plenum chamber arranged to receive pressurized fluid from the master cylinder by way of a conduit extending through a bell which contains the clutch and the slave cylinder. The annular piston of the slave cylinder surrounds the input shaft of the transmission. The plastic material of the casing of the slave cylinder can contain one or more additives which enhance its strength and/or influence its frictional engagement with the adjacent surfaces of the piston or of a lip seal which reciprocates with the piston. The piston and/or the lip seal can be installed in the casing to contact one or two metallic or plastic guide sleeves which are connected to or form part of the casing.

CROSS-REFERENCE TO RELATED CASES

This application is a divisional application of U.S. patent applicationSer. No. 10/794,568, filed on Mar. 4, 2004, which is a divisionalapplication of U.S. patent application Ser. No. 10/087,439, filed onFeb. 21, 2002 which is a continuation of international application Ser.No. PCT/DE00/02739, filed Aug. 11, 2000, which is hereby incorporated byreference in its entirety, and claims the priority of the commonly ownedGerman patent application Serial No. 199 40 024.5 filed Aug. 24, 1999.The disclosure of the above-referenced commonly owned copending Germanpatent application, as well as that of each US and foreign patent andpatent application identified in the specification of the presentapplication, is incorporated herein by reference.

BACKGROUND OF THE INVENTION

The invention relates to improvements in hydraulic operatingarrangements, particularly to operating arrangements for clutches in thepower trains of motor vehicles. More particularly, the present inventionrelates to improvements in hydraulic operating arrangements which can beutilized with advantage in or in combination with so-called master andslave cylinders to actuate friction clutches between the prime movers(such as internal combustion engines) and the change-speed transmissionsin the power trains of motor vehicles.

Published German patent application No. 197 42 468 discloses a clutchoperating arrangement wherein the housing or casing of the slavecylinder consists, at least in part, of a plastic material. Such slavecylinders are known as central clutch release devices and their casingsare normally affixed to the transmission housing or case by threadedfasteners. At least a part of the casing of the slave cylinder ismounted in such a way that it surrounds the input shaft of thechange-speed transmission. Securing of the casing of the slave cylinderto the transmission case by threaded fasteners during assembly of thepower train is time consuming and hence expensive.

Presently known seals, such as lip seals, which serve to seal theinternal chamber of the casing of the slave cylinder from the atmospherewhen such chamber is to receive hydraulic fluid from the master cylinderare normally mounted on the reciprocable piston in the slave cylinder ofa brake actuator. Such seals share the axial movements of the piston andare called upon to move along inner and outer sealing surfaces which arerespectively provided on a metallic and on a plastic material. Thesealing surface which is provided on a plastic material normally offersa greater frictional resistance to axial movements of the piston and islikely to generate noise while guiding a piston during actuation (suchas disengagement) of the friction clutch.

It is also known to provide the slave cylinder in the hydraulic clutchactuating system of the power train in a motor vehicle with an internalsleeve which serves to guide the piston of the slave cylinder and ismade of steel or an equivalent material. A drawback of such slavecylinders is that adequate sealing of the contact surface(s) between theguide sleeve of steel and the plastic casing of the slave cylinder cancreate serious problems. In order to avoid such problems (including highcost or an unsatisfactory seal), the casings or cylinders of manypresently known slave cylinders do not employ separately produced guidesleeves for the piston, i.e., the guide sleeve is part of the plasticcasing. A drawback of such proposals is that the making of a slavecylinder casing without a separately produced guide sleeve for thepiston but with an adequate guide surface for the piston (i.e., with aguide surface provided on a part made of a plastic material) cannot bemade at a reasonable cost in available machines, e.g., in standardinjection molding machines for the making of articles from plasticmaterial. As a rule, an injection molding machine which is to turn outsuch plastic slave cylinder casings must be equipped with highly complexparts such as shifting or pushing arrangements and the like.

OBJECTS OF THE INVENTION

An object of the present invention is to provide a slave cylinder,especially a slave cylinder which can be used as a friction clutchrelease unit in the power train of a motor vehicle, which does notexhibit the aforediscussed drawbacks of conventional slave cylinders andwhich exhibits numerous important advantages over such conventionalparts or groups of parts.

Another object of our invention is to provide a slave cylinder which canbe turned out in large numbers in conventional injection molding andother available machines.

A further object of the invention is to provide a slave cylinder whichcan be integrated into existing types of power trains without any orwithout appreciable modifications of such power trains.

An additional object of the invention is to provide a slave cylinderwhich can be installed within the clutch bell under the hood of a motorvehicle.

An additional object of the invention is to provide a slave cylinderwhich requires a minimum of maintenance, no inspection or infrequentinspection, and whose useful life is longer than that of presently knownslave cylinders for use as a means for actuating friction clutches inthe power trains of motor vehicles.

Still another object of the instant invention is to provide a hydraulicclutch actuating system the condition and mode of operation of which canbe expected to remain unchanged during the useful life of the motorvehicle.

A further object of the invention is to provide a slave cylinder whichcan be readily sealed where necessary, wherein the casing is in optimalfrictional engagement with the piston, which is not subject to excessivewear, the material of which is not likely to exhibit pronounced fatigueafter relatively short periods of use, and which can be made of a widevariety of readily available materials.

Another object of the invention is to provide a hydraulic operatingarrangement which employs the above outlined slave cylinder.

A further object of the present invention is to provide novel andimproved adapter means for use in the connection between a mastercylinder and a slave cylinder in the power train of a motor vehicle.

An additional object of the invention is to provide novel and improvedmethods of making various component parts of the means for actuating thefriction clutch in the power train of a motor vehicle.

Still another object of the invention is to provide novel and improvedmaterials and/or combinations of materials for the making of casingswhich are to form part of slave cylinders in the power trains of motorvehicles.

A further object of the invention is to provide novel and improved meansfor ventilating the chambers of cylinders or casings forming part ofslave cylinders.

SUMMARY OF THE INVENTION

One feature of the present invention resides in the provision of asystem for altering the bias of a clutch spring (such as a diaphragmspring) in and for thus changing the condition of an engageable anddisengageable friction clutch between a rotary output element (such as acrankshaft or a camshaft) of a prime mover (such as an internalcombustion engine) and a rotary input element of a change-speedtransmission preferably having a composite housing or case and beingdisposed in the power train of a motor vehicle. The improved systemincludes a primary unit (such as a master cylinder) having an output,means (such as a clutch pedal or an electronic actuator) for actuatingthe primary unit to thus transmit a pulse by way of the output of theprimary unit, a clutch release device having an at least partiallyplastic composite casing and a mobile bearing coaxial with the inputelement of the transmission and arranged to alter the bias of the clutchspring in response to movement axially of the input element, means foroperatively connecting the output of the primary unit with the clutchrelease device to move the bearing axially of the input element inresponse to actuation of the primary unit to transmit a pulse by way ofthe output, and means for coupling the clutch release device to acomponent of the transmission housing which is preferably locatedopposite the bearing.

The means for actuating the primary unit (such as the aforementionedmaster cylinder) can comprise a driver-operated pedal (clutch pedal) inthe motor vehicle.

The coupling means which connects the clutch release device with acomponent of the transmission housing can include a self-lockingarrangement.

The aforementioned master cylinder can constitute a first hydrauliccylinder and piston unit of the improved system, and the aforementionedoutput can constitute an outlet of the cylinder of the first unit. Thecasing of the clutch release device can include or constitute thecylinder of a second hydraulic cylinder and piston unit having a mobilepiston which is operatively connected with the bearing and isreciprocable in the casing. The actuating means of the improved systemcan include a conduit which connects the outlet of the cylinder of thefirst unit with the cylinder of the second unit.

The coupling means of the improved system can comprise complementaryfirst and second coupling members which are form-lockingly connected toeach other and are respectively provided on the housing and on thecasing. The second coupling member can be of one piece with the casing,and such casing can constitute an injection molded part. The secondcoupling member can have a shape which is imparted thereto exclusivelyby injection molding.

It is also possible to employ coupling means which includes at least onesnap fastener. The housing of such system is preferably coaxial with thecasing and the snap fastener can include at least one hook provided onthe housing or on the casing and at least one opening receiving the atleast one hook and provided either in the casing or in the housingagainst axial movement relative to the housing. Alternatively, the atleast one snap fastener can comprise an annular array of male fasteningelements provided on one of the casing and housing and at least onefemale fastener provided in the other of the casing and housing andreceiving the male fastening elements. The at least one female fastenercan include an annular array of openings, at least one for each of themale fastening elements.

The casing of the clutch release device can include a cylinder and thisdevice can further comprise an annular piston which is provided in thecylinder and is arranged to move the bearing relative to the inputelement (such as a shaft) of the change-speed transmission. The bearingand the piston of such clutch release device surround the input elementof the transmission.

Another feature of the present invention resides in the provision of adevice which is set up to operate a clutch (such as a friction clutch)between a prime mover and a change-speed transmission in the power trainof a motor vehicle. The improved device comprises an axial extensionwhich is provided on the case or housing of the transmission and has aradially inwardly extending circumferetially segmented (subdivided orpartitioned) profile, and a casing having an enlarged portion projectingradially outwardly of and overlying (i.e., being surrounded by) at leasta portion of and engaging the extension by snap action or an analogousor equivalent action to thus secure the casing to the transmission caseas seen axially as well as radially of the extension.

A further feature of our invention resides in the provision of a devicefor operating a clutch between a prime mover and a change-speedtransmission in the power train of a motor vehicle. The device includesan axial extension provided on the transmission case and having aradially extending profile which is provided with a circumferentiallyextending groove, and a casing having an enlarged portion overlapping orbeing overlapped by a portion of the extension and engaging the latterby snap action. The engaging means includes at least one fastener whichextends into the aforementioned groove of the axial extension of thetransmission case.

An additional feature of the instant invention resides in the provisionof a device for operating a clutch between the prime mover and thechange-speed transmission in the power train of an automobile or anothertype of motor vehicle. The device comprises an axially enlarged tubularextension provided on the transmission case and having a segmentedexternal profile, and a casing having at least one snap fastener whichprojects radially inwardly of the extension and engages the externalprofile to thus secure the casing to the transmission case.

The external profile of the tubular extension can define an annularrecess, and the at least one snap fastener extends into the annularrecess of the external profile.

The casing of the device includes a portion which is received in thetubular extension, and the aforementioned portion of the casing canfurther serve as a means for centering the casing relative to theextension.

Another feature of our invention resides in the provision of a devicefor operating a clutch between a prime mover and a change-speedtransmission in the power train of a motor vehicle. The improved clutchoperating device comprises a casing including a portion confronting apart of the transmission case, and at least two substantially pin-shapedprojections which are provided on the casing and are received incomplementary recesses provided therefor in the aforementioned part ofthe transmission case. The projections have deformable portionsextending into the respective recesses and frictonaly engaging theaforementioned part of the transmission case.

The deformable portions extend radially beyond the respectiveprojections and the openings can be dimensioned in such a way that theyreceive the respective projections with lateral play but effectdeformation of deformable portions in response to insertion of theprojections into the respective openings so that the deformable portionsare self-lockingly retained in the respective openings. The dimensionsof the deformable portions (each such deformable portion can include oneor more elastic laminations) can decrease in directions as seen into therespective openings.

An advantage of the just described embodiment is that the pin-shapedprojections can cooperate with the aforementoned part of thetransmission case to hold the casing and the case against axial andangular movement relative to each other. Furthermore, the openings (suchas blind holes) can be provided in the casing and the projections arethen provided on the transmission case. It is also possible to provideone or more projections on the casing and to further provide one or moreprojections on the transmission case. The deformable portions canconstitute washer-like resilient components which surround therespective pin-shaped projections.

All of the projections may but need not be identical and the radiallyouter portion of each washer-like deformable portion can be providedwith cutouts to facilitate flexing of such deformable portions duringinsertion into the respective openings.

The just described mode of non-rotatably coupling two parts to eachother with simultaneous holding of the parts against axial movementrelative to each other can be utilized with advantage in numerousdevices or arrangements other than those which serve to releasablycouple parts in a clutch actuating device for use in the power trains ofmotor vehicles.

An additional feature of our invention resides in the provision of ahydraulically actuatable slave cylinder unit for operating a clutchbetween a prime mover and a change-speed transmission in the power trainof a motor vehicle. The improved slave cylinder unit comprises a plasticcasing, a guide sleeve which is provided in the casing and surrounds theinput shaft of the transmission, an annular piston which is reciprocablein an annular chamber of the casing and surrounds the sleeve, aclutch-operating release bearing which is provided in the chamber and isaffixed to the piston, and means for securing the sleeve to thetransmission case or to the casing. The means for securing includes aradially outwardly extending flange which is provided at one end of thesleeve and is adjacent the transmission case. The flange has a radiallyouter portion which is received in a groove of the casing, and thesecuring means further includes at least one retaining member which isprovided in the casing and cooperates with the radially outer portion ofthe flange to hold the casing and the sleeve agains axial movementrelative to each other.

The radially outer portion of the flange can include an annular array ofextensions which form part of a bayonet mount of the at least oneretaining member.

Furthermore, the at least one retaining member can form an integral partof the casing and can be deformed to overlie the radially outer portionof the flange subsequent to insertion of the radially outer portion intothe groove.

The at least one retaining member can be deformed as a result of atreatment preferably involving hot caulking or ultrasonic caulking.

The guide sleeve can be received in the casing in stressed condition,and this guide sleeve can cooperate with the casing to jointly definethe annular chamber. The improved slave cylinder unit can furthercomprise at least one sealing element which is interposed between thecasing and the sleeve. Such at least one sealing element can constitutean O-ring, a flat seal, a liquid seal or a flow seal. The flow seal canconsist of or include a solidified flowable substance which is receivedin an annular groove of the casing; such solidified flowable substancecan consist of or contain silicon rubber or silicon resin. This flowseal can be disposed radially outwardly of the chamber and the casingcan be provided with at least one inlet for admission of the flowablesubstance into its groove. The groove for the flowable substance canhave a diameter which slightly exceeds the diameter of the chamber.

The flow seal can have a ring-shaped sealing surface and the casing canbe provided with an axially raised sealing surface which surrounds theinlet, which is engaged by the flow seal, and which is in sealingengagement with the radially outer portion of the sleeve.

The slave cylinder unit can further comprise a stop for the releasebearing or the piston, and such stop is or can be remote from theaforementioned flange. For example, the stop can be of one piece withthe sleeve and can be arranged to prevent disengagement of the pistonand of the bearing from the sleeve in storage and/or during transport ofthe casing, e.g., from the manufacturing plant to the automobileassembly plant.

The stop can constitute a deformed portion of the sleeve; for example,such stop can include at least one substantially radially outwardlyextending tongue of the sleeve and such tongue can extend at leastsubstantially circumferentially of the sleeve.

The guide sleeve can consist, at least in part, of a plastic materialand the stop can be of one piece with such guide sleeve and/or with thecasing.

Another feature of the invention resides in the provision of ahydraulically operated disengaging system for a friction clutch in thepower train of a motor vehicle wherein the clutch is installed between aprime mover and a change-speed transmission. The improved systemcomprises a master cylinder unit, a slave cylinder unit which includes acasing and an annular piston which is reciprocable in an annular plenumchamber of the casing, means for conveying pressurized hydraulic fluidfrom the master cylinder unit into the plenum chamber, and an annularlip seal provided in the chamber and being slidable relative tocylindrical internal and external surfaces which are provided within thecasing radially outwardly and inwardly of the chamber. The casingincludes at least one cylindrical metallic sleeve and one of theaforementioned surfaces is provided on the at least one sleeve.

The arrangement can be such that the external surface is provided on thesleeve.

The casing can comprise two cylindrical metallic sleeves one of which isprovided with the internal surface and the other of which is providedwith the external surface.

The at least one sleeve can consist, at least in part, of aluminum,steel, titanium and/or the alloys of such metals.

Furthermore, the at least one sleeve can include a film which isprovided with the at least one surface and serves to reduce thecoefficient of friction between the at least one sleeve and the lipseal. The film can contain or consist of grease or of a metal ennoblingmaterial.

The at least one sleeve can be provided with a substantially radiallyoutwardly projecting extension and the lip seal is then disposed in thechamber between the piston and the extension. The latter has a sealingsurface which abuts a plastic portion of the casing, and suchdisengaging system can further comprise a second seal which isinterposed between the plastic portion of the casing and the extension,a cover which overlies the extension opposite the second seal, and meansfor securing the cover to the plastic portion of the casing. Suchsecuring means can include an at least substantially annular joint whichcan be a welded joint, an adhesive joint or a detent.

Still another feature of our invention resides in the provision of ahydraulically operated disengaging system for a friction clutch in thepower train of a motor vehicle wheren the clutch is installed to operatebetween a prime mover and a change-speed transmission. The improvedsystem comprises a master cylinder unit and a slave cylinder unit whichlatter includes a composite casing consisting at least in part of aplastic material. The slave cylinder unit further includes an anularpiston which is reciprocable in an annular plenum chamber of the casingand the latter includes at least two sections which are separable or areseparately produced parts to facilitate sealing of the chamber from theatmosphere. Such disengaging system further comprises means forconveying pressurized hydraulic fluid from the master cylinder unit intothe annular plenum chamber; the conveying means includes at least oneextension provided on the casing.

The extension can include a pipe which is provided with at least onechannel for delivery of pressurized fluid from the master cylinder unitinto the chamber. The casing can be of one piece with the pipe, and suchpipe as well as the casing can consist of a plastic material. Thedisengaging system can further comprise a bell which confines thefriction clutch and the slave cylinder unit. The pipe extends from themaster cylinder unit through and into the bell.

The extension can include a nipple and a conduit which is coaxial withand communicatively connects the nipple with the plenum chamber.

The casing can include a wall which is adjacent an end of the chamberand has an opening for the flow of fluid from the conduit into thechamber. This casing can constitute an injection molded product and canbe provided with at least one aerating port. Such disengaging system canfurther comprise means for sealing the at least one port; such sealingmeans can be secured to the casing by welding, threading, the use ofadhesive and/or by latching with the interposition of at least onesealing element between the casing and the sealing means.

A further clutch disengaging system which embodies the present inventioncomprises a master cylinder unit and a slave cylinder unit including acasing and an annular piston which is reciprocable in an annular plenumchamber of the casing. The casing consists, at least in part, of aplastic material, and the system further includes means for conveyingpressurized hydraulic fluid from the master cylinder unit into thechamber and at least one sensor which is associated with the casing andserves to monitor the positions of the piston in the chamber. Forexample, the sensor can be set up to monitor distances which are coveredby the piston in the chamber. Such sensor can be at least partiallyembedded in the casing, and such casing can constitute an injectionmolded article. The means for conveying can include a tubular extensionof the casing, and such system can further comprise conductor meanswhich is or are embedded in the extension and is or are connected withthe at least one sensor.

Another embodiment of the improved hydraulically operated clutchdisengaging system comprises a master cylinder unit and a slave cylinderunit which includes a casing and an annular piston slidably reciprocablein an annular chamber of the casing. The casing consists at least inpart of a plastic material and contains at least one component whichserves to reduce sliding friction with the piston, and the systemfurther comprises means for conveying pressurized hydraulic fluid fromthe master cylinder unit into the plenum chamber.

The sliding friction reducing component can consist of graphite and/or apolyfluorohydrocarbon; such component can constitute between about 5%and 20%, preferably between 8% and 15% of the material of the casing. Asatisfactory casing can contain between about 35% and 75% of a plasticmaterial (such as a thermoplastic or thermosetting substance), betweenabout 20% and 45% of fibers (such as glass fibers which strengthen thecasing), and between about 5% and 20% of sliding friction reducingmaterial.

A further embodiment of the improved hydraulically operated clutchdisengaging system can comprise a master cylinder unit and a slavecylinder unit which latter includes a casing having an annular plenumchamber, an annular piston reciprocable in the chamber, a firstcylindrical surface surrounding the chamber, a second cylindricalsurface surrounded by the chamber, and an annular lip seal which isdisposed in the chamber, which sealingly engages the two surfaces andwhich is reciprocable with the piston along and in sealing engagementwith predetermined portions of the two surfaces. The slave cylinderfurther comprises a metallic film provided at least on the predeterminedportion of at least one of the surfaces, and the clutch disengagingsystem further comprises means for conveying pressurized hydraulic fluidfrom the master cylinder into the plenum chamber.

A further embodiment of the improved clutch disengaging system comprisesa master cylinder and a slave cylinder including a casing and a metallicsleeve which is received in and defines with the casing and annularchamber. The sleeve has limited freedom of radial movement relative tothe chamber and the slave cylinder further comprises an annular pistonwhich is reciprocably received in the chamber and an annular lip sealwhich is reciprocable in the chamber with the piston and has an internalsurface which sealingly engages the sleeve and an external surface whichsealingly engages the casing. The disengaging system further comprisesmeans for conveying pressurized hydraulic fluid from,the master cylinderinto the annular chamber.

A further fluid-operated clutch actuating system of the presentinvention compriss a master cylinder, and a slave cylinder including acasing defining a chamber and a piston which is reciprocable in thechamber to thus effect actuation of the clutch. The clutch actuatingsystem further comprises means for conveying fluid between the mastercylinder and the chamber of the casing in the slave cylinder. The fluidconveying means comprises an aerating device with at least one sealableport for evacuation of fluid from the chamber.

Another fluid-operated clutch actuating system of the present inventioncomprises a master cylinder unit and a slave cylinder unit including apreferably plastic casing and a piston which is reciprocable in achamber of the casing to thus actuate the clutch. The actuating systemfurther comprises means for conveying fluid from the master cylinderunit into the chamber to thus move the piston relative to the casing,and such fluid conveying means includes an adapter which is separablyconnected with the master cylinder unit and/or with the slave cylinderunit.

The novel features which are considered as characteristic of theinvention are set forth in particular in the appended claims. Theimproved clutch actuating system itself, however, both as to itsconstruction and the modes of assembling, installing and operating thesame, together with numerous additional important and advantageousfeatures and attributes thereof, will be best understood upon perusal ofthe following detailed description of certain presently preferredspecific embodiments with reference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a partially schematic and partially sectional view of a powertrain which is embodied in a motor vehicle and wherein the frictionclutch between the prime mover and the change-speed transmission of thepower train can be actuated by a hydraulic central clutch release systemor device embodying one form of the present invention;

FIG. 2 is an enlarged view of a detail within the phantom-line circle IIshown in FIG. 1;

FIG. 3 is an axial sectional view of a portion of a central clutchrelease system constituting a first modification of that shown in FIG. 1and an axial sectional view of a first arrangement for securing theclutch release system to the case of a change-speed transmission in thepower train of a motor vehicle;

FIG. 4 is an elevational view of a portion of a third central clutchrelease device and a partly elevational and partly sectional view of adifferent connection between the transmission case and the clutchrelease device;

FIG. 5 is a fragmentary axial sectional view of a fourth central clutchrelease device, the lower part of the piston in the slave cylinder unitin this device being shown in one end position and its upper part beingshown in the other end position;

FIG. 6 is an enlarged view of a detail within the phantom-line circle VIshown in FIG. 5;

FIG. 7 is an axial sectional view analogous to that of FIG. 5 butshowing a fifth central clutch release device;

FIG. 7 a is an enlarged view of a detail of a gluide sleeve constitutinga first modification of the guide sleeve in the clutch release deviceshown in FIG. 7;

FIG. 7 b is a view similar to that of FIG. 7 a but showing a secondmodification of the guide sleeve shown in FIG. 7;

FIG. 8 is a fragmentary axial sectional view of certain parts of afurther central clutch release device with one embodiment of guide meansfor the piston of the slave cylinder unit;

FIG. 9 is a fragmentary axial sectional view of a slave cylinderconstituting a modification of that shown in FIG. 8;

FIG. 10 is an axial sectional view of the casing of a further centralclutch release system;

FIG. 11 is a fragmentary axial sectional view of a modified annularpiston for use in the central clutch release system of the presentinvention;

FIG. 12 is a similar fragmentary axial sectional view of a furtherpiston;

FIG. 13 is a similar fragmentary axial sectional view of an additionalpiston;

FIG. 13 a is a fragmentary axial sectional view of a piston constitutinga modification of that shown in FIG. 13;

FIG. 14 is a sectional view of a further central clutch release systemwith the piston shown in two different axial positions;

FIG. 15 is an enlarged view of the detail within the phantom-line circleXV in FIG. 14;

FIG. 16 is a fragmentary axial sectional view of a central clutchrelease device with a sensor built into its casing;

FIG. 17 is an axial sectional view of an adapter which can be utilizedas a component of means for connecting a master cylinder unit with aslave cylinder unit in the power train capable of utilizing a centralfriction clutch release device of the present invention;

FIG. 18 is a similar sectional view of a modified adapter;

FIG. 19 is a similar sectional view of a third adapter;

FIG. 20 a is an axial sectional view of an aerating valve which can beutilized in conjunction with the central clutch release device or systemof the present invention;

FIG. 20 b illustrates the valve of FIG. 20 a but with the piston-likevalving element in a different axial position;

FIG. 21 a is an axial sectional view of a second aerating valve;

FIG. 21 b illustrates the structure of FIG. 21 a but with thepiston-like valving element in a diferent axial position;

FIG. 22 a is an axial sectional view of a third aerating valve whichconstitutes a modification of that shown in FIGS. 21 a and 21 b;

FIG. 22 b illustrates the structure of FIG. 22 a but with thepiston-like valving element in a different axial position;

FIG. 23 a is an axial sectional view of a fourth aerating valve;

FIG. 23 b shows the structure of FIG. 23 a but with the piston-likevalving element in a different axial position;

FIG. 24 a is an axial sectional view of a fifth aerating valve;

FIG. 24 b illustrates the structure of FIG. 24 a but with thepiston-like valving element in a different axial position;

FIG. 25 is an end elevational view of still another central clutchrelease or disengaging device or system;

FIG. 26 is an enlarged fragmentary sectional view substantially as seenin the direction of arrows from the line XXVI-XXVI shown in FIG. 25;

FIG. 27 is an end elevational view of a further clutch release device;

FIG. 28 is an enlarged fragmentary sectional view substantially as seenin the direction of arrows from the line XXVIII-XXVIII of FIG. 27;

FIG. 29 is a partly end elevational and partly sectional view of anadditional clutch release or disengaging device; and

FIG. 30 is an enlarged fragmentary axial sectional view substantially asseen in the direction of arrows from the line XXX-XXX in FIG. 29.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows a portion of a power train for use in a motor vehicle, andmore particularly a system 1 for altering the bias of a clutch spring 4(such as a diaphragm spring) and for thus changing the condition of anengageable and disengageable friction clutch 3 between a rotary outputelement 2 a of a prime mover 2 and a rotary input element 8 of achange-speed transmission 2 b having a composite housing or case 9 andbeing disposed in the power train of the motor vehicle. The prime mover2 can constitute an internal combustion engine or a hybrid motor, andits rotary output element 2 a can constitute a camshaft or a crankshaftserving to transmit torque to the input shaft 8 of the change-speedtransmission 2 b by way of the engageable/disengageable friction clutch3 which is installed in a stationary outer housing or bell 2 c.

The system 1 for altering the bias of the clutch spring 4 includes aprimary unit here shown as a master cylinder 70 having a housing orcylinder 70 a and a piston 70 b which is reciprocable in the housing 70a by a piston rod 70 c. The latter is normally maintained in a retractedposition (e.g., by a spring or in any other suitable manner) but can hemoved forwardly by actuating means here shown as a clutch pedal 72. Thiscauses the piston 70 b to expel pressurized hydraulic fluid from achamber 70 d of the housing 70 a by way of an outlet or output 70 e andinto a conduit 71 which connects the master cylinder 70 with a centralclutch disengaging or release device 5 here shown as including a slavecylinder having a plastic casing 10, a reciprocable annular piston 10 asurrounding the input element 8 of the transmission 2 b, and a releasebearing 5 a borne by the piston 10 a. The piston 10 a and the releasebearing 5 a are coaxial with the input shaft 8 of the transmission 2 b.

Depending upon the exact nature of the clutch 3 (whether mechanicallyoperated by the operator of the motor vehicle or automated), themechanical actuating means (pedal) 72 for the piston 70 b in the housing70 a of the master cylinder 70 can be replaced with another suitable(other than hydraulic) actuator such as an electric, pneumatic or hybridactuator. The same applies for the clutch release device 5, i.e., thisdevice can include any suitable centrally located arrangement which candisengage the friction clutch 3 by changing the bias of the clutchspring 4 in response to axial movement of the release bearing 5 a.

The central clutch release or disengaging device 5 has an axialextension 6 which is received in an opening 7 of the compositetransmission housing or case 9 and surrounds the input shaft 8. A formlocking connection 11 between the transmission case 9 and the casing 10of the central clutch release device 5 is designed to couple the parts5, 10 together with a self-locking action and includes one or more malecomponents extending into one or more windows, apertures or openings 12provided in the transmission case 9.

The details of one presently preferred self-locking coupling means 11are shown in FIG. 2. Such coupling means comprises radially inwardlyextending tongues or prongs or arms 13 forming part of or affixed to theplastic casing 10. The number of tongues 13 can vary within a widerange, e.g., between 2 and 8, preferably between 2 and 3, and suchtongues are preferably equidistant from each other as seen in thecircumferential direction of the transmission case 9. The tongues 13 canbe received in the respective openings 12 by snap action. Such openingsare provided in an axial extension 7 a of the transmission case 9. Theform-locking connection is established in response to pushing of thetongues 13 axially of the coaxial shafts 2 a and 8 and into the openings12. It will be appreciated that other types of automatic (self-locking)coupling action can be resorted to for the establishment of a reliable,long-lasting and compact connection between the transmission case andthe clutch release bearing 5 a.

The character la denotes in FIG. 1 an assembly which includes thefriction clutch 3 and the hydraulic system 1 and is installed in partwithin an in part outside of the bell 2 a.

FIG. 3 shows a modified central clutch disengaging or release device 105having a plastic casing 110 with an axial extension 106 including a deepdrawn cylindrical guide sleeve 114 which is form-lockingly connectedwith the transmission case 109 by extending into an opening 107 of thelatter. In order to prevent axial movements of the device 105 relativeto the transmission case 109, the structure including the parts shown inFIG. 3 comprises a self-locking connection 111 including a snap fastenerhaving an annular array of first coupling members in the form ofhook-shaped projections 113 provided on the casing 110 and extendinginto second coupling members having openings or apertures 109 machinedinto or otherwise formed in a collar 109 a of the transmission case 109.

Another self-locking connection 211 between the casing 210 of the clutchrelease or disengaging device 205 and the transmission case 209 is shownin FIG. 4. The casing 210 has axially parallel pins or studs 213 each ofwhich carries a set of resilient flexible radially outwardly extendinglaminations 213 a which are deformed in response to insertion of pins213 into complementary openings or recesses or apertures 212 in theadjacent surface of the transmission case 209. The laminations 213 athen establish form-locking connections with the surfaces 212 a boundingthe apertures 212 to thus reliably couple the casing 210 to thetransmission case 209. When the self-locking connecting means 211 isoperative, the laminations 213 a of each set form substantially tubularbodies which at least partially overlie each other and frictionallyengage the surfaces 212 a surrounding the respective apertures 212. Thearrangement can be such that the diameters of the laminations 213 a ofeach set decrease in a direction from the casing 210 toward the tips 213b of the respective pins 213; this facilitates the introduction of pins213 into the respective apertures 212.

FIG. 5 shows a central clutch release device 305 with a casing 310 whichis preferably made of a plastic material and contains a preferablymetallic cylindrical guide sleeve 314. For example, the sleeve 314 canbe made in a deep drawing machine. That end of the sleeve 314 which isadjacent the transmission is provided with a radially outwardlyextending washer-like enlarged portion or flange 315 which, in turn, hasan axially extending radially outermost portion 316 (see also FIG. 6).The portion 316 extends toward the engine (not shown in FIG. 5) of themotor vehicle and into a groove 317 of the plastic casing 310 of theclutch release device 305. In order to establish a connection which iseffective in the axial direction, the portion 316 has radial extensions318 which project radially outwardly into segments 318 a of the groove317. Retaining members 320 are provided in the radial segments 318 a tohold the respective extensions 318 therein. The retaining members 320form part of a bayonet mount which holds the guide sleeve 314 and itsflange 315 against axial movement relative to the plastic casing 310.The radial segments 318 also form part of the bayonet mount andcooperate with the adjacent retaining members 320 to maintain thebayonet mount in the operative position.

A sealing ring 319 is provided and acts as an annular seat between theradial flange 315 and its radially outermost portion 316 on the onehand, and the plastic casing 310 on the other hand. The retainingmembers 320 can be embedded into the plastic casing 310 during themaking of such casing, e.g., in an injection molding machine.Alternatively, the members 320 can be affixed to the casing 310 byresorting to a plastic processing technique such as hot caulking,ultrasonic caulking or the like. The guide sleeve 314 can be a tight fitin the casing 310 and can be centered in the latter.

The connections which are shown in FIGS. 5 and 6 constitute but twoexamples of connections between the metallic sleeve-like guide 314 andthe plastic casing 310. Moreover, the connections which are actuallyshown in FIGS. 5 and 6 can be utilized jointly with one or moreadditional connections such as with axially extending fasteners,radially notched nails, standard rivets and/or blind rivets and thelike. It is also possible to provide the parts 314 and 310 with matingthreads, e.g., by resorting to self-tapping threads. Such self-tappingthreads can be employed, for example, to threadedly connect the flange315 to the casing 310. In addition to or in lieu of such threadedconnection, the portion 316 of the flange 315 can be provided with aradially extending threaded portion and/or with radially extendingconnectors in the form of fasteners.

It is further advisable to provide a tangential connection which securesthe guide sleeve 314 to the casing 310 and which can include atensioning sleeve, not shown. Still further, the groove 317 can receiveone or more inserts which serve as reinforcements and/or as retainingmeans to ensure the establishment of a reliable form-locking connectionbetween the guide sleeve 314 and the casing 320 in addition to or inlieu of the aforedescribed undertakings. It has been found that anultrasonic welded joint or a hot hammer tightening is particularlysuitable to secure the guide sleeve 314 to the casing 310; such jointcan be established between the flange 315 or its portion 316 and thecasing 310. An advantage of the just discussed undertakings is that oneneed not resort to a bayonet mount including the parts 318 and 320; allthat is necessary is to introduce the portion 316 of the flange 315 intothe groove 317 and to secure the portion 316 by ultrasonic weldingand/or hot hammering.

FIG. 7 shows a central clutch release device 405 having a plastic casing410 and a guide sleeve 414 made of a metallic material, as well as anaxially reciprocable annular piston 425 which cooperates with the parts410, 414 to define an annular chamber 427. The piston 425 carries anannular lip seal 426 with radial and axial play; this lip seal serves toseal the chamber 427. The lower half of the piston 425 is shown in theextended position, and the upper part of this piston is shown in theretracted position.

The lip seal 426 engages a first sealing surface 428 which surrounds theannular chamber 427, and a second sealing surface 429 provided at theexterior of the guide sleeve 414 and being surrounded by the chamber427. The structure which is shown in FIG. 7 preferably further includesa second metallic guide sleeve 430 which is provided with the firstsealing surface 428 and cooperates with the guide sleeve 414 to form acylinder for the piston 425. The sleeve 430 can be made of aluminumsheet or steel sheet. The provision of the metallic outer guide sleeve430 is desirable and advantageous because its sealing action with thelip seal 426 is similar or identical to that between the seal 426 andthe radially inner guide sleeve 414. It has been ascertained that asealing action directly between the lip seal 426 and the plastic casing410 (i.e., the seal which is established between the parts 426 and 410if the metallic sleeve 430 is omitted) is much inferior to that betweenthe sleeve 430 and the lip seal 426. Inferior sealing action between thelip seal 426 and the plastic casing 410 is attributable to the presenceof micropores in the plastic material and the tendency of the seal 426to adhere to the material of the casing 410.

Furthermore, the utilization of a metallic sleeve 430 renders itpossible to dispense with the expensive and time-consuming inspection ofthe internal surface of the casing 410 for possible presence ofmicropores and the treatment of such internal surface for the purpose ofsealing the micropores (if any). Still further, it is not necessary toeffect accelerated setting or hardening of the plastic material of thecasing 410 for the purpose of reducing the likelihood of presence ofmicropores in the surface which is overlapped by the novel metallicsealing sleeve 430.

The sleeve 430 cooperates with a sealing ring 431 to seal the plenumchamber 427 from the surrounding atmosphere. That portion of the sleeve430 which is adjacent the sealing ring 431 is provided with a radialextension 432 a which latter locates it relative to a radial extension416 of the guide sleeve 414 and a radially extending portion 433 a ofthe casing 410.

The means for supporting and centering the clutch release device 405includes an extension 427 a of the portion 416 at one axial end of theguide sleeve 414. The other axial end of the guide sleeve 414 isprovided with a stop 450 for the piston 425. Such stop can be replacedwith one or more stops (not shown) for the clutch release bearing 451which shares the axial movements of the piston 425. The diaphragm spring(shown at 4 in FIG. 1) of the friction clutch 3 urges the pressure plate3A of the clutch against the clutch disc 3B to thus maintain the clutchin the engaged condition (in which the clutch can transmit torquebetween the output element 2 a of the engine 2 and the input element 8of the transmission 2 b) when the prongs of the diaphragm spring 4 arenot depressed by the bearing (such as the bearing 451 shown in FIG. 7).The coil spring 452 of FIG. 7 reacts against the casing 410 of theclutch release device 405 and bears upon the bearing 451 which isconnected with the piston 425; this coil spring cooperates with the stop450 to limit the extent of axial movability of the piston 425 in adirection to the left (as viewed in FIG. 7) before the structure of thisFigure is assembled with the friction clutch, i.e., before the bearing451 can bear upon the tips of prongs of the diaphragm spring. This isdesirable during transport of the device 405 to the locale of actualuse.

The stop 450 is preferably of one piece with the guide sleeve 414. Ifthe sleeve 414 is made of a metallic material, the stop 450 canconstitute one radially ouwardly deformed end portion of the metallictube which is converted into the sleeve 414. Alternatively, and as shownin FIG. 7a, one end portion of the guide sleeve 414 can be provided withone, two or more (e.g., several equidistant) tongues 452 a which replacethe stop 450 of FIG. 7. The tongue 452 a which is shown in FIG. 7 aextends crcumferentially of the guide sleeve 414. On the other hand, thetongue 452 b of FIG. 7 b extends axially of the guide sleeve 414. It isadvisable to provide the free end of each tongue 452 b with at least oneradial extension 452 c which is axially offset relative to the majorpart of the guide sleeve 414 to thus contribute to a reduction of axiallength (axial space requirements) of the part 452 b shown in FIG. 7 b.

If the guide sleeve 414 is made of a plastic material and is of onepiece with the casing 410 of the clutch release device 405, itstongue(s) or stop(s) 450, 452 a or 452 b can be made at the time theguide sleeve is being made in an injection molding or other suitablemachine. In the event of an inspection, maintenance or replacement, thepiston 425 and/or the release bearing 451 can be separated from thecasing 410 without necessitating even partial deformation or destructionof such parts. The just described mode of assembling the piston and therelease bearing with the casing of the central clutch release device canbe resorted to in the power train which employs the structure of FIG. 7,7 a or 7 b as well as in many power trains which employ central clutchrelease devices other than those shown in and described with referenceto these Figures.

FIG. 8 shows a further embodiment of a sealing sleeve 430 without aradial extension. This sleeve extends essentially along the entire pathof axial movement of the lip seal 426 and is or can be recessed radiallyinto the plastic material of the casing 410. Alternatively, thestructure of FIG. 8 can comprise a self-locking arrangement (not shown)which can serve as a snap fastener to lock the sleeve 430 to the casing410. It is of particular advantage to embed the sealing sleeve 430 intothe casing 410 already during the making of the latter; a presentlypreferred undertaking is to make the casing 410, and to simultaneouslyembed the sleeve 430 therein, in an injection molding machine. In orderto establish a desirable sealing action, the sleeve 430 can be glued tothe plastic casing 410; in addition to or in lieu of such undertaking,one can employ one or more suitably configurated separately producedsealing elements in the form of rings or the like.

The casing 410 a portion of which is shown in FIG. 8 consists of asuitable synthetic plastic material. Thus, this casing can embody anintegral part corresponding to the separately produced metallic guidesleeve 414 of FIG. 7. Such casing can be produced in an injectionmolding machine. In order to enhance the sealing action at its internalsealing surface 429 which is adjacent the internal surface of theplastic cylindrical piston 425, one can employ a metallic sleeve 432which is surrounded by the piston 425 as well as by the lip seal 426 andcan be made of the same material as the guide sleeve 430 which surroundsthe parts 425 and 426.

The casing 410 is made entirely of a suitable synthetic plastic materialand can be utilized with or without the sealing sleeve 430 and/or 432.As already mentioned hereinbefore, an injection molding procedure is thepresently preferred method or process of making the casing 410 of FIG. 8as well as the casings shown in FIGS. 1 to 7. However, it is oftenpreferred to utilize the plastic casing 410 in conjunction with at leastone of the guide sleeves 430 and 432. The surface 428 of the guidesleeve 430 and/or the surface 429 of the guide sleeve 432 can be readilyfinished to a degree which is desirable or necessary or indispensablefor the establishment of an optimum sealing engagement with the piston425 and/or with the lip seal 426.

FIG. 9 shows a portion of a plastic casing 410 which forms part of acentral clutch release device and is connected with a metallic guidesleeve 414 having a radially outwardly extending portion 416 which abutsa shoulder 410 a of the casing 410. A cover 434 in the form of a ringserves to hold the sleeve 414 against axial movement in a direction tothe left, as viewed in FIG. 9, i.e., against movement relative to thecasing 410 and toward the prime mover if the structure shown in FIG. 9is installed in the power train of a motor vehicle of the charactershown (in part diagrammatically and in part in axial sectonal view) inFIG. 1.

The plenum chamber 427 which surrounds the metallic sleeve-like guide414 in the casing 410 is sealed in part by a lip seal 426 and in part byan annular axially acting sealing ring 434 received in a groove of thecasing 410 adjacent the inner side of a radially outwardly extending endportion 416 of the guide sleeve 414 at the shoulder 410 a. Theplate-like cover 433 fully overlies the outer side of the radiallyoutwardly extending stop or cover or extension 416 of the guide seeve414 and is secured to the casing 410 against axial movement relativethereto. Furthermore, the cover 433 is fitted into an annular recess atthe right-hand end face of the casing 410 against radial movementrelative to the casing. The exact mode of connecting the cover 433 tothe casing 410 is not critical; for example, one can resort toultrasonic welding, to hot caulking, an adhesive, ultrasonic caulking, aform-locking procedure such as frictional fitting into each other and/orothers.

The embodiments of the casing 410 which are shown in and which weredescribed hereinbefore with reference to FIGS. 8 and 9 exhibit theimportant advantage that the guide sleeve 430 and/or 432 and/or 414 isnot subjected to undesirable and/or excessive tensional stressing, forexample, axial stressing relative to the slave cylinder casing 410and/or vice versa. This, in turn, enhances the stability (sturdiness) ofthe structure embodying the casing 410 when the hydraulic clutchactuating system is in use.

It is often of advantage to treat the surface(s) of the sleeve 430and/or 432 shown in FIG. 8 for the purpose of enhancing the tribologicalcharacteristics of such sleeve or sleeves and/or to impart suchcharacteristics thereto, i.e., the ability to stand pronounced friction,the ability to undergo satisfactory lubrication and/or the ability tostand extensive and/or pronounced wear upon the surface(s) in relativemotion. It has been ascertained that guide sleeves 430 and/or 432 whichare made of steel can enhance the rigidity of the entire casing 410and/or of the combination(s) of parts including such casing.

If the plastic casing 410 of FIG. 9 is self-lockingly coupled with theguide sleeve 414 already during assembly of the clutch releasing ordisengaging system, and if the plate-like cover 433 of FIG. 9 isinstalled with requisite play relative to the radial extension or stop416 so that it abuts the transmission case (not shown in FIGS. 8 and 9),one can avoid an indirect or direct contact between the guide sleeve 414and the transmission case. In order to further damp the contact betweenthe plate-like cover 433 and the case of the change-speed transmission 2b, the structure of FIG. 9 uses the sealing ring 435. An undulatesealing ring 436 (shown in FIG. 9), such as a suitable annular shaftseal, can be provided to surround the input shaft of the change-speedtransmission (see the shaft 8 in the embodiment of FIG. 1). The shaftseal can be held in proper position by snap action and can be made of asuitable plastic material as a sandwich structure, as a composite sealor in many other suitable ways.

FIG. 10 illustrates a preferably plastic casing 510 for use in a centralclutch disengaging or release device and surrounds a cylindrical guidesleeve (not shown) to define therewith an annular plenum chamber for areciprocable annular piston connected to a release bearing, e.g., in amanner as shown in FIG. 5 or 7. The annular plenum chamber is surroundedby a cylindrical sealing surface 528 of the casing 510. The surface 528is engaged by a lip seal, e.g., a lip seal of the type shown at 426 inFIG. 7, which seals the plenum chamber radially outwardly.

In order to enhance the sealing action, the surfaces can be coated witha film of metallic material, e.g., in a manner as proposed in publishedGerman patent application No. 43 31 728. This publication proposes theapplication of a coat of nickel, namely chemical nickel coating inaccordance with the autocatalytic technique. When applied in conjunctionwith the structure shown in FIG. 10, the film or coat 540 is limited tothat portion of the internal surface of the casing 510 which is incontact with the lip seal while the latter moves axially between its twoend positions. An advantage of limited coating with a film of metallicmaterial is that it entails substantial savings in such material andhence a reduction of cost of the entire clutch actuating arrangement.

A minimizing of the application of nickel or other suitable metallicmaterial to the surface or surfaces coming into actual contact with thelip seal is desirable and advantageous on the additional ground thatthis reduces te likelihood of contact between human skin and the appliedmetallic layer; such contact could result in damage to the skin and thelikelihood of such contact is greatly reduced if the coating is limitedto operations in a manner and in the regions as pointed outhereinbefore. Another suitable undertaking is zinc phosphating of thatportion of the surface of the casing 510 which comes in contact with thelip seal.

A suitable method which can be resorted to in connection with metalcoating one or more selected portions of the casing 510 is to stack aplurality of such casings axially next to each other (such as on top ofeach other) and to thereupon equalize the intermediate regions at 540 a,540 b with spacing elements in the form of rings. The ringssimultaneously serve to respectively fix and seal the neighboringcasings relative to and from each other. This results in theestablishment of a column of superimposed (aligned) casings and ringswhich preferably define an upright cylindrical space ready to bethereupon filled with liquefied metal-containing material serving toprovide the desired metallic film on those portions of the superimposedcasings which are to be contacted by the lip seals in actual use of thecasings.

FIGS. 11 to 13 a illustrate several embodiments of pistons (427 a, b, cand d) corresponding to (i.e., serving the same purpose as) the piston425 in the structure shown in FIG. 7. As a rule, such pistons are madeof fiber-reinforced synthetic plastic materials, e.g., in an injectionmolding machine. In the absence of armoring with films of a metallicmaterial, plastic pistons are likely to chock (wedge or block or jam)when in contact with a sealing surface (such as the sealing surfaceshown at 428 in FIG. 7).

In order to enhance the slidability of a plastic piston along a sealingsurface (such as of the piston 425 along the sealing surface 428 shownin FIG. 7), it is advisable to incorporate (compound) into the plasticmaterial of the casing 410 one or more suitable slidability enhancingsubstances, such as graphite and/or PDFE, which are admited into theplastic material prior to the carrying out of the injection moldingoperation. For example, the plastic material of the casing 410 shown inFIG. 7 can contain not less than 10% graphite and then preferablycontains less than the usual percentage (between 35% and 45%) ofreinforcing fibrous material. Alternatively, the omitted percentage ofstandard reinforcing material can be replaced with mineral fibers. Thebasic material of the casing 410 is or can be a thermoplastic substance(such as PA (polyamide), PPA, PPS, PBT (polybutylene ephtalate) or thelike) or a thermosetting substance (e.g., a phenolic resin). It has beenascertained that a satisfactory plastic material has an expansioncoefficient not or not appreciably affected by temperature changes; forexample, the glass temperature TG is above 100° C.

In addition to the above enumerated and discussed alternatives andmodifications regarding its composition, the piston of the improvedslave cylinder unit whose cylinder or housing includes the casing, suchas the casing 510, can assume any one of a host of various shapes fourof which are shown in FIGS. 11, 12, 13 and 13 a. The piston 427 b ofFIG. 12 has end faces 450 a, 450 b at least one of which (see theright-hand end face) is profiled at 450 b′. The illustrated profile is arather pronounced bevel or facet; however, such profile need not beexactly flat but can have a convex, undulate or any other suitable shapewhich enhances a particular characteristic (such as slidability) of thepiston.

The piston 427 c of FIG. 13 exhibits all features of the piston 427 bshown in FIG. 12 and its end faces 450 a, 450 b are respectivelyprovided with circumferentially complete or interrupted annular orarcuate relief notches, grooves or recesses 450 c, 450 d surroundingannular portions 450 e, 450 f which enhance the radial elasticity oryieldability of the respective parts of the piston 427 c at itscylindrical internal surface 427 c′. One of the recesses 450 c,450 d canbe omitted or one of the end faces 450 a, 450 b can be provided with twoor more circumferentially complete or arcuate grooves which can beshort, very short, relatively long or very long. The numbers, thedimensions and/or the configurations of the recesses 450 c, 450 d willdetermine the elasticities and/or other desirable characteristics of thecorresponding portions 450 e, 450 f of the piston 427 c. As a rule,greater elasticity of the piston at its end faces (especially close toits internal surface 427 c′) reduces the likelihood of undesirabledisfiguration and resulting jamming of the piston in the cylinder orhousing of the slave cylinder unit.

The piston 427 c of FIG. 13 is not or need not be considered as havingbeen drawn to scale. For example, the width of the annular portion 450 eand/or 450 f need not exceed and can be less than 1 mm (as measuredradially of the piston 427 c), as long as such annular portions satisfytheir intended purpose of reducing the likelihood of jamming of thepiston 427 c in the cylinder.

The substantially cylindrical piston 427 a which is shown in FIG. 11 isprovided with several (e.g., with an annular array of) preferably butnot necessarily equidistant pockets 450 g each of which can constitute astorage facility or reservoir for a lubricant (e.g., grease). Suchlubricant is automatically distributed along the external and on theinternal surface of the piston 427 a when the latter is caused orpermitted to move along the surface(s) of the adjacent part or parts,for example, part(s) consisting at least in part of a synthetic plasticmaterial. It is often sufficient to replace the illustrated throughpockets 450 g with relatively shallow or relatively deep “blind” pocketswhich are provided in the internal or in the external surface of thepiston 427 a. The making of pockets which extend radially of and all theway through the piston 427 a is often preferred for convenience ofmanufacture.

It is also within the purview of the present invention to confine inone, more or all pockets 450 g bodies of sponge-like material whichserves to reliably hold lubricant in the respective pockets and/or toconfine in the respective pockets a lubricant having a relatively lowviscosity, i.e., a lubricant which, in the absence of sponge-likeforaminous fillers, would be unlikely to dwell in the pockets. It isalso possible to provide the piston 427 a with one or more covers orlids (not shown) serving to overlie the radially outer or inner end orends (normally the outer end or ends) of the respective pocket(s) 450 g.Still further, it is possible to provide the piston 427 a with at leastone pocket having an open radially outer end and with at least onepocket having a closed radially inner end; for example, the piston 427 acan have at least one annular array of pockets with open radially innerends and at least one annular array of pockets with open radially outerends. In accordance with a presently preferred embodiment, the piston427 a can be provided with at least one annular array of preferablyequidistant pockets which are open at their radially inner and radiallyouter ends and each of which contains a piece of sponge permeated with amass of lubricant; such piston further carries closures (such as flapsof sheet-like material) which overlie and seal the radially outer endsof the pockets and are bonded or otherwise reliably (removably or moreor less permanently) affixed to the piston.

FIG. 13 a shows a portion of an annular piston 427 d which is producedin accordance with the so-called mono sandwich process. Thus, thispiston has a core 427 d′ consisting of a high-stability plastic materialsuch as a thermoplastic or thermosetting synthetic plastic substancewhich can be reinforced, e.g., with glass fibers. The radially outer andinner portions 427 d″, 427 d′″ of the piston 427 d can be made of aplastic material which exhibits a high coefficient of friction and/or ahigh surface quality or finish, for example, a polymer of a fluorocarbonsuch as PTFE, PFA, PVDF, non-reinforced plastic materials which cancontain slip additives (antiseize agents) such as graphite, PTFE and thelike. Such design and composition of the piston 427 a ensure that thecoefficient of friction between the piston and the casing of the centralclutch disengaging or release device will be more satisfactory than inthe absence of such additives, i.e., that the piston will offer a lesserresistance to sliding relative to its cylinder.

Pistons 427 d of the type shown in FIG. 13 a can be produced in specialinjection molding machines wherein discrete first and second extrudersfurnish the first and second constituents of the plastic material. Itgoes without saying that such special injection molding machines canalso serve as a means for producing casings such as those denoted byreference characters 410, 510 and 610 and respectively shown in FIGS. 7,10 and 14; the casings may but need not be equipped with integratedguide sleeves. The arrangement can be such that the surfaces which areto be contacted by the lip seal are provided on a plastic materialhaving a low coefficient of friction but the remaining part or parts ofthe casing can be made of a plastic material exhibiting a pronouncedresistance to deformation.

FIG. 14 illustrates a central clutch disengaging or releasing device 605having a plastic casing 610 of one piece with a conduit or pipe 610 apreferably made of a synthetic plastic material in an injection moldingmachine. Such mode of making the casing 610 is relatively expensive;therefore, it might be advisable to employ a composite casing which isassembled of two or more discrete sections. This renders it possible toprovide the casing 610 with the required channels (such as the mutuallyinclined communicating channels 649, 648 and with the chamber 627 whichcommunicates with the fluid supplying channel 649 by way of theintermediate channel 648) by resorting to appropriate injection moldingimplements. It is presently preferred to assemble the casing of at leasttwo discrete injection molded components which are produced separatelyand are thereupon assembled into the structure denoted by the referencecharacter 610.

In accordance with a modification, the sleeve-like part 614 can beproduced separately of the remainder of the casing 610 and is thereuponaffixed to the casing 610, preferably in the region C shown in FIG. 14.This simplifies the making of the conduit 648 which merely necessitatesthe use of a core in the injection molding implement. The separatelyproduced sleeve 614 and the remainder of the casing 610 are thereuponsecured to each other by resorting to conventional welding, bondingand/or caulking procedures.

FIG. 14 further shows an annular piston 625 which is reciprocable in theannular plenum chamber 627 and carries a lip seal 626. The sleeve 614and the remainder of the casing 610 are joined by a wall 610 b boundingthat end of the chamber 627 which is remote from the engine (not shownin FIG. 14). The channel 648 connecting the channel 649 with the chamber627 communicates with an opening 651 a in the wall 610 b; such openingreceives a core which forms part of the injection molding tool and isnecessary in the course of the injection molding operation to form thechannel 648. The opening 651 a is closed by a component part in the formof a plug 651 shown in FIG. 15.

The detail within the circle XV in FIG. 14 is shown in FIG. 15 drawn toa larger scale. The casing 610 is of one piece with the guide sleeve 614and is provided with the channel 649 discharging into the channel 648which is parallel to the axis of the passage defined by the sleeve 614.The channel 648 is outwardly adjacent the external sealing surface 628and communicates with the plenum chamber 627. Such one-piece casing 610cannot be produced in a standard injection molding machine. Therefore,one must resort to an undertaking which involves the making in thecasing 610 of an opening 651 a as an axial extension of the channel 648,and such opening 651 a is thereupon sealed by a plug 651 (FIG. 15),e.g., by resorting to ultrasonic welding, to an adhesive, to caulking,hot caulking or the like. It is also possible to employ between the plug651 and the casing 610 a discrete sealing element, such as a sealingring. The extension of the channel 648 projects radially inwardly andserves to convey pressurized fluid into the plenum chamber 627.

Referring again to FIG. 14, the provision of the channels 649, 648 whichlead to the plenum chamber 627 exhibits the advantage that theycontribute to a lengthening of the path for the piston 625 and for thelip seal 626 which is form-lockingly associated with the piston. Thiscontributes to a pronounced increase of the overall space for travel ofcasing 610 and to a simultaneous reduction of space requirements of theentire clutch disengaging structure.

The channel 649 is disposed axially between the piston 625 and thechannel 627. The partial axial guidance of the fluid supplying channel648 around the radially outermost sealing surface 628 (see also FIG. 15)renders it possible to reduce the space requirements, as seen in theaxial direction, and hence the overall length of the clutch releasedevice 605. This, in turn, renders it possible to reduce the cost andthe space requirements of the entire prime mover of the motor vehicle.

FIG. 14 further shows a radially outwardly extending stop 650 whichreplaces the stop 450 of the metallic sleeve 414 shown in FIG. 7 and isan integral part of (i.e., of one piece with) the casing 610. Thus, suchstop 650 can be provided during the making of the casing 610 in aninjection molding machine and can exhibit a certain amount ofelasticity. The stop 650 can also serve as a safety enhancing componentduring transport of the casing 610 and it can constitute acircumferentially complete ring or an annular array of discretesections. If the piston 625 (with the bearing 605 a) and/or the lip seal626 is to be mounted on or removed from the sleeve 614, the stop 650 orits sections undergoes or undergo temporary deformation to thereuponsnap back to the position(s) shown in FIG. 14.

The central clutch release device 705 of FIG. 16 is designed for use inconjunction with automated clutches and/or automated change-speedtransmissions and is integrally associated with a detector or sensor704. The latter serves to monitor the extent of release movement of therelevant part or parts of the clutch. This sensor can be integrated intothe casing 710 of the clutch release device 705 during making of thecasing in an injection molding machine, for example (and as shown), inthe region of the guide sleeve 714 or in the region of the outer sealingsurface 728.

It is often desirable to provide the radially inner part of the sensor704 with a metallic shell and to secure it, not unlike a metallic guideshell, at the inner circumference of the release device 705, e.g., bysnap action, by resorting to an adhesive or in another suitable manner.The sensor 704 is sealed from the plenum chamber 727 and can include ametallic wall which cooperates with the lip seal 726 to enhance thesealing action. The conductor means 704 a leading to and/or from thesensor 704 can be embedded in the injection molded plastic material ofthe casing of the central clutch release device 705. The terminals 704 bof such conductor means are shown as being located at the inlet 710 awhich admits pressurized fluid into the elongated channel defined by thecasing 710 and leading to the plenum chamber 726. The terminals 704 bcan be affixed to a plug (not shown) which enters a socket when thecasing 710 is properly secured to a friction clutch. The plug for theterminals 704 b can be disposed between the inlet 710 a and an outlet(not shown) of a fluid evacuating conduit which is or can be disposed atthe level of the inlet 710 a.

The sensor 704 can include an electric coil which ascertains the axialmovements of the piston 725 and release bearing 711 as a result ofchanges of an electrical value, e.g., of an electric or magnetic fieldwhich varies in response to axial displacement of the piston in itschamber 726. The piston 725 disengages the friction clutch (not shown inFIG. 16) by way of the release bearing 711 in a manner as alreadydescribed hereinbefore. An advantageous signal evaluating procedure caninvolve an eddy current procedure, a process of measuring the inductance(and more specifically changes of inductance) in dependency upon theextent and/or direction of movement of the piston 725 and/or others.

FIGS. 17 to 19 illustrate three embodiments of an adapter which cancouple the housing or cylinder of a master cylinder unit with thehousing or casing or cylinder of a slave cylinder unit (such as thatincluding the casing 710 shown in FIG. 16). Reference may be had, forexample, to FIG. 1 wherein an adapter 71 a is installed in thestationary outer housing or bell 2 c to connect the plastic casing ofthe clutch release device 5 with the master cylinder 70 by way of theconduit 71. An adapter is particularly desirable and advantageous whenthe configuration of channels in the clutch housing must conform to thatof the master cylinder and the conduit(s) which is or which are locatedoutside of the clutch bell. Otherwise stated, an adapter can simplifythe establishment of a connection between the casing of a clutch releasedevice and the housing of a master cylinder with a minimum ofmodifications of mass-produced parts which serve to actuate a frictionclutch in response to depression of a clutch pedal (72) or in responseto activation of an actuator which can be utilized in conjunction withautomated or automatic friction clutches, e.g., in the power train of amotor vehicle. The adapter can be installed in the bell 2 c of FIG. 1 toconnect the clutch release device 5 (which is confined in the bell) withthe conduit 71 leading from the master cylinder unit 70 which latter islocated outside of the bell.

Prior proposals include the utilization of angular adapters which areexpensive and include housings that are forged, at least in part. As arule, it is necessary to subject such conventional adapters to atreatment in at least-two axial directions. On the other hand, theadapters 850 a, 850 b and 850 c which are respectively shown in FIGS.17, 18 and 19 are built linearly.(i.e., they are straight) and,therefore, can be made and finished (treated) in a relatively simplemanner and in a single axial direction. In addition, the weight of theadapter 850 a, 850 b or 850 c can be a fraction of the weight of aconventional adapter.

The adapter 850 a of FIG. 17 includes a housing 852 a having an internalthread 851 a mating with the external thread of a conduit 810 acorresponding to the conduit 71 shown in FIG. 1, i.e., leading to theoutlet 70 e of the chamber 70 d in the housing 70 a of the mastercylinder 70. The conduit 810 a is configurated in such a way that it canextend through an opening in the bell 2 c, i.e., into the interior ofsuch bell. The conduit 810 a has a hexagonal head 810 a′ so that it canbe conveniently threaded into the housing 852 a (at 851 a). Thereference character 853 a denotes in FIG. 17 a sealing shoulder which isprovided in the housing 852 a and bears upon the adjacent annularshoulder at the right-hand end face of the conduit 810 a. The conduit810 a and the housing 852 a are or can be made of a metallic material.Sealing engagement at the shoulder 853 a involves a plastic deformationof the part 810 a and/or 852.

Surplus liquid can be evacuated from the path defined by the coaxialpassages of the parts 810 a, 852 a by loosening the threaded connectionat 851 a to thus establish communication between the interior of theconduit 810 a and a radial opening or port 858 a of the housing 852 a.Such possibility of aeration of the axially extending passages in theconduit 810 a and the housing 852 a constitutes an advantageous featureof the adapter 850 a; this renders it possible to evacuate spent orsurplus pressure fluid from the interior of the adapter 850 a.

The character 854 a denotes in FIG. 17 a nipple which facilitatescoupling of the housing 852 a to the outlet of the cylinder in a mastercylinder unit which serves to supply pressurized fluid to the cylinderof the slave cylinder unit. A clamp 856 a (or a set of such clamps) isprovided on the housing 852 a to couple the nipple 854 a to suchhousing. The nipple 854 a has a suitable socket or detent for each clamp856 a of the housing 852 a. A sealing ring 855 a is installed betweenthe nipple 854 a and the housing 852 a.

The modified adapter 850 b of FIG. 18 has a conduit 810 b which is astraight piece of piping and is of one piece with the nipple 854 b whichis connectable directly to the outlet of the cylinder or housing of amaster cylinder unit (such as the unit 70 shown in FIG. 1) or with aconduit 71 corresponding to the similarly referenced conduit shown inFIG. 1. The adapter 850 b further comprises a box nut or union nut 858 bwhich cooperates with a sealing ring to normally seal a port 858 b′ inthe nut from the passage for the flow of hydraulic fluid between thecoaxial passages in the parts 810 b and 71. The annular sealing shoulder853 b is effective when the union nut 858 b is tightened so that itseals a second port 858 b′ from the surrounding atmosphere. The port 858b′ is provided in the nipple 854 b and communicates with the port 858 bwhen the union nut 858 b is loosened so that the passage in thecomponent parts 810 b, 854 b can communicate with the atmosphere. Part855 is a sealing ring.

The adapter 850 c of FIG. 19 is preferably made of a plastic materialand operates without a sealing shoulder (such as 853 a or 853 b). Thesealing member is replaced with sealing rings 853 c, 855 c which arerecessed into the nipple 854 c within the nut 858 c. The latter ispreferably made in an injection molding machine. The pipe 858 c′replaces the part 858 b′ and cooperates with the port in one of thecomponent parts 810 c, 854 c when the nut 858 c is loosened.

A system which employs one of the adapters 850 a (FIG. 17), 850 b (FIG.18) and 850 c (FIG. 19) can be constructed and assembled and can operateas follows: The slave cylinder unit can consist of a plastic material oris diecast of aluminum or is produced in accordance with anothersuitable technique and is preferably part of a central clutchdisengaging or release device. It is devoid of connectors to conduitsbut is equipped with a fluid supplying box which sealingly and fixedlyreceives the conduit 810 a, 810 b, 810 c or an analogous component partleading to or constituting an element of the slave cylinder unit. Thechannel in the conduit (such as 810 a) preferably communicates with anopening or with openings provided in conventional clutch disengagingsystems without the need for a modification of such conventionalsystems. All that is necessary is to properly select the dimensions ofthat part or those parts of the adapter whose conduit (such as 810 a) isto be received in the opening(s) of a conventional system. The conduit(such as 810 a) of the improved adapter is fitted into the justdiscussed opening(s) of the conventional system and the nipple (such as854 a) is connected with the outlet of the master cylinder unit 70 orwith the conduit 71. If the clutch release device which employs theimproved adapter 850 a, 850 b or 850 c does not have its own aeratingarrangement, such function is performed by the parts including the port858 a, 858 b′ or 858 c′, i.e., the respective union nut is loosened torender the port 858 a or 858 b′ or the pipe 858 c′ and port 858 c″ (FIG.19) effective.

FIGS. 20 a to 24 b illustrate several embodiments of an aeratingarrangement for a slave cylinder. The aerating arrangement is directlyconnected to the slave cylinder. FIGS. 20 a, 21 a, 22 a, 23 a and 24 ashow the respective aerating arrangements in operative positions, andthe FIGS. 20 b, 21 b, 22 b, 23 b and 24 b illustrate the correspondingaerating arrangements in those positions they assume when the respectiveclutch disengaging or release systems or devices are operative and noaeration is possible.

The aerating arrangement 901 of FIG. 20 a includes a housing or case 903preferably consisting of a synthetic plastic material and including aconnector 902 which is to be attached to the cylinder or casing of theslave cylinder. The housing 903 further includes a fluid supplyingchannel 904 and a fluid discharging nipple 905. A stepped central hole906 of the housing 903 receives a piston 907 which is movable axiallyagainst the opposition of an axially acting resilient element 908 hereshown as a coil spring. The piston 907 is provided with a steering edge909 and with a radially outwardly extending cylindrical guide 910 whichis confined to axial movements in a larger-diameter portion 906 a of thecentral hole 906. Another portion of the piston 907 is movable withclearance in a smaller-diameter portion 906 b of the central hole sothat the piston and the housing section surrounding the portion 906 bdefine an annular passage or clearance 911 for the flow of fluid. Whenthe piston 907 assumes the retracted position of FIG. 20 b, the annularclearance 911 is seated by a ring-shaped sealing element 912.

When the piston 907 assumes the aerating position of FIG. 20 a, thefluid can flow through the clearance 911, along the steering edge 909and on to the outlet (nipple) 905. A distancing element or stop 913 isprovided to abut and stop the piston 907 in the aerating position ofFIG. 20 a; at such time, a further sealing ring 914 is active betweenthe piston 907 and the distancing element 913. The piston 907 is notfixed in the aerating position of FIG. 20 b and, therefore, must bemaintained under pressure.

When in the operative position of FIG. 20 b, the piston 907 is biased bythe coil spring 908 so that its hook-shaped detent or detents 915 bearsor bear upon one or more shoulders in a notch 916 or in several discretenotches of the housing 903.

FIGS. 21 a and 21 b show an aerating device 1001 which is identical withthe aerating device 901 with the exception of the detent arrangement forthe piston 1007. The latter is provided with two notches 1017, 1018either or which can receive a retaining clamp 1019 of or in the housing1003. When the piston 1007 assumes the aerating position of FIG. 21 a,the clamp 1019 extends into the notch 1018. This clamp extends into thenotch 1017 in the operative position of the piston. It is not necessaryto permanently bias the piston 1007 during aeration.

FIGS. 22 a and 22 b show an aerating device 1001′ which is at leastsubstantially identical with the aerating device 1001 of FIGS. 21 a and21 b except that the energy storing device (corresponding to the coilspring 908 shown in FIGS. 20 a to 21 b) is omitted. The piston 1007′ isor can be identical with the piston 1007 in the housing 1003 of FIGS. 21a and 21 b.

The aerating device 1101 of FIGS. 23 a and 23 b comprises a piston 1107having an axial aerating passage 1107 a which corresponds to thatdefined by the nipple 905 of FIGS. 20 a and 20 b.

FIGS. 24 a and 24 b show an aerating arrangement 1201 for a slavecylinder which does not have a discrete aerating conduit. The piston1207 is part of the conduit 1120 which supplies pressurized fluid fromthe master cylinder, not shown. A retaining clamp 1219 (corresponding tothe part 1019 shown in FIGS. 21 a and 21 b) is provided to hold thepiston 1207 (i.e., the conduit 1120) in either of the two axialpositions determined by notches in the housing of the aeratingarrangement 1201. Aeration takes place under the action of hydrostaticpressure. It is to be noted that the conduit 1120 is to be guided to thehighest point of the plenum chamber in the slave cylinder.

FIG. 25 illustrates a plastic casing 1310 for a central clutch releasedevice which constitutes or includes a slave cylinder in a hydraulicclutch actuating system, and FIG. 26 shows the complete central clutchrelease system 1305 in a cross-sectional view.

The casing 1310 is similar to the casing 110 in the central clutchdisengaging or release device 105 shown in FIG. 3; it comprises a guidesleeve 1314 which is connected with the main portion of the plasticcasing 1310 in a manner analogous to that already described inconnection with FIG. 3. A difference exists in the manner ofestablishing a sealing engagement between the main portion of theplastic casing 1310 and the sleeve-like guide 1314; this modifiedsealing engagement can be used with advantage in any other slavecylinder or in many other slave cylinders having a corresponding guidesleeve. The sealing action is furnished by a flat sealing ring 1350, asubstantially annular abutment surface 1353 in the casing 1310, and byan essentially plane engagement (at 1352) of the guide sleeve 1314. Theabutment surface 1353 is coaxial with and surrounds the axis of theguide sleeve. The ring-shaped seal 1350 is recessed into the surface1353 and is at least substantially aligned with the radially outercylindrical wall 1328 in the plenum chamber 1327 which receives thepiston 1325 and the lip seal 1326 which is affixed to the piston. Theseal 1350 overlies an opening 1348 which is provided radially outwardlyof the chamber 1327 and supplies fluid from the supply channel 1349 inthe plastic casing 1310. The central clutch release device 1305 can beaerated by way of the channel 1349.

The connection between the opening 1348 and the plenum chamber 1327 isestablished by way of at least one but preferably two or more grooves1356 extending axially between the abutment surface 1353 and the sealingring 1350. The seal for the plenum chamber 1327, as well as for thesupply channel 1349, from the atmosphere is established by an axiallyraised endless bead 1351 which is provided at the abutment surface 1353of the casing 1310 and the smallest radius of which corresponds to thatof the internal surface of the casing 1310. The bead 1351 is larger (asseen radially) only at the opening 1348 and extends around this opening.Such arrangement ensures that the pressure acting upon the sealing ring1350 in the plenum chamber 1327 is much lower, i.e., the establishmentof a seal between the sleeve-like guide 1314 and the casing 1310presents fewer problems.

Another desirable feature, which can be of advantage in all slavecylinders having discrete guide sleeves, is that the guide sleeve 1314is movable radially of the casing 1310. This results in theestablishment of a clearance or play (at 1310 d) between the guidesleeve 1314 and the radial abutment surfaces 1310 c, 1314 c respectivelyprovided on the casing 1310 and on the guide sleeve 1314.

Still another embodiment of a sealing arrangement between the casing1410 of the central clutch release device 1405 and a guide sleeve 1414is shown in FIGS. 27 and 28. With the exception of the seal between theguide sleeve 1414 and the casing 1410 and the establishment of a plenumchamber 1427, the structure shown in FIGS. 27 and 28 is or can beidentical with that shown at 1305 and 1310 in FIGS. 25 and 26. Thecasing 1410 is provided with an axially extending groove 1451 which isadjacent the internal surface of the casing 1410 (as seen in the radialdirection of the guide sleeve 1414). A sealing rib 1451 a is providedbetween the internal surface 1410 a and the groove 1451 a. The sealingring 1451 is expanded and surrounds the discharge opening 1448 at theend of the passage 1449. The groove 1451 receives a standard O-ring.1450 which establishes a seal between the casing 1410 and the guidesleeve 1414. It is often of advantage to make the groove 1451 wider (asseen in the radial direction of the guide sleeve 1414) than necessaryfor insertion of the O-ring 1450 and to remove the entire sealing rib1451 a at a specific location or at several locations or to removesegments of such sealing rib (as seen in the circumferential directionof the internal surface 1410 a). This results in the establishment of anaccurately defined clearance 1415 b which is disposed between the casing1410 and the guide sleeve 1414 and provides a path for the flow ofhydraulic fluid to and from the passage 1449. The dimensions of theclearance 1451 b are or can be selected in such a way that the extent ofcompression of the O-ring 1450 as a result of engagement of the casing1410 with the guide sleeve 1414, and hence a change of such clearance,are negligible or insignificant.

The guide sleeve 1414 is fastened and centered by an axial extension1410 b of the casing 1410. To this end, the guide sleeve 1414 isdeformed in the axial direction at the periphery of the radial marginalzone 1416 and toward the passage 1449, and is secured to the extension1410 b by a self-locking device 1411 which can constitute a snapfastener and/or can include an array of rivets, threaded fasteners, abayonet mount or the like to hold the guide sleeve 1414 against any oragainst any undesired axial and/or angular movements.

FIGS. 29 and 30 show a further embodiment of a central clutch releasedevice 1505 which can constitute or include a slave cylinder. Thecharacters 1552, 1553 denote the outlets of two channels 1549 a, 1549 bwhich are provided in the preferably plastic casing 1510, and morespecifically in a pipe-like extension 1510 a which can form part of oris affixed to the casing 1510. The channel 1549 a serves to conveypressurized hydraulic fluid, and the channel 1549 b is a fluidevacuating channel. The piston 1525 is reciprocable in the plenumchamber 1527 between the external surface of the guide sleeve 1514 andthe internal surface of the adjacent cylindrical internal portion of thecasing 1510. The piston 1525 is reciprocable with the lip seal 1526, andthis lip seal engages the internal surface of the radially innermostportion of the casing 1510 as well as the external surface of the guidesleeve 1514.

The outlets 1552, 1553 of the channels 1549 a, 1549 b communicate with acommon chamber or compartment 1551 located radially of and communicatingwith the plenum chamber 1527. The outlets 1552, 1553 are segregated fromeach other by a barrier 1550 which is received in the compartment 1551and at least substantially seals the channels 1549 a, 1549 b from eachother. When the channel 1549 b is free to evacuate fluid from thechamber 1527 by way of an opened or loosened aerating screw, such fluidflows from the channel 1549 a and through the plenum chamber 1527 intothe evacuating channel 1549 b to be flushed out of the chamber 1527 whennecessary. Such arrangement also permits for evacuation of air bubblesand/or for more effective evacuation of aged hydraulic fluid (if any)from the plenum chamber 1527.

The barrier 1550 can be retroactively fitted into certain existing typesof slave cylinders and can be made of any one of a great variety ofdifferent materials, e.g., an elastic material (such as rubber or EPDM)or a plastic or metallic or other suitable part which conforms to thecompartment 1551 to establish a seal between the outlets 1552, 1553. Itis also possible to form the barrier 1550 during making of the casing1510, e.g., in an injection molding machine. It is equally possible toprovide the barrier 1550 with one or more holes which open in responseto the application of elevated pressures, e.g., while the release deviceis in the process of disengaging the friction clutch, so that fluid canflow between the outlets 1552 and 1553. This excludes the undesirableinfluence of hysteresis and the like. When the pressure in thecompartment 1551 drops, such apertured barrier can at leastsubstantially seal the channels 1549 a, 1549 b from each other.

The flow of pressurized fluid from the compartment 1551 into the chamber1527 can be optimized by providing the guide sleeve 1514 with a radiallyoutwardly and thereupon axially extending profile 1555. Such profile canbe provided with grooves associated with the channels 1549 a, 1549 b orit can be provided with additional or discrete grooves which aredistributed in the circumferential direction. The just described designsof axial profiles can be resorted to with advantage in conjunction withall or practically all or many slave cylinders having guide sleeves andchannels leading to a plenum chamber adjacent the guide sleeve. Suchdesign entails savings in space (as seen in the axial direction of theguide sleeve), allows for more satisfactory supplying of pressurizedfluid, as well as numerous additional important advantages.

The entire disclosures of published German patent applications Nos. 19849 850.0 and 198 16 255 are incorporated herein by reference.

The improved clutch operating arrangement is susceptible of numerousadditional modifications without departing from the spirit of thepresent invention. For example, and referring again to FIG. 4, theopenings 212 can constitute tapped bores and the pins 213 can constituteor include externally threaded parts which serve to secure the casing210 to the transmission case 209. Such fasteners can be provided withwasher-like laminations 213 a which contribute to retention of thecasing 210 in an optimum position relative to the transmission case. Thepins 213 and the laminations 213 a can also serve as a means forcentering the casing 210 relative to the transmission case 209. Themarginal portions of the washer-like laminations 213 a can be providedwith radial cutouts or slots to facilitate their deformation duringintroduction of the pins 213 into the respective openings or apertures212. It is also possible to provide the openings 212 in the casing 210and to mount the pins 213 on the transmission case. Still further, eachof the parts 209, 210 can be provided with openings as well as withpins. The pins are preferably equidistant from each other (as seencircumferentially of the casing 210) and can serve to hold the parts209, 210 against angular and axial movement relative to each other aswell as to center the casing of the slave cylinder relative to thetransmission case.

The openings 212 can receive reinforcing sleeves which, in turn, receivethe pins 213 or their equivalents. The openings and the reinforcingsleeves can be provided on the casing 210 or on the radial extension(such as 315) of the sleeve (314), and the pins or their equivalents arethen used to secure the casing of the slave cylinder to the transmissioncase by way of the radial extension of the sleeve.

The guide sleeve (such as the sleeve 114 shown in FIG. 3) can serve tocenter the casing (110) relative to the transmission case (109) and canbe provided with means (such as a bayonet mount of the type shown inFIG. 6) for separably coupling the casing to the transmission case aswell as for centering the casing relative to the transmission case. Thesleeve 114 can directly surround the input shaft (shown at 8 in FIG. 1)of the transmission (2 b).

The parts of the bayonet mount shown in FIG. 6 can be finished prior toattachment of the guide sleeve 314 to the casing 310; alternatively,certain parts of such bayonet mount or an equivalent thereof can beobtained by deforming the radial extension 318 and/or the retainingmember(s) 320 subsequent to introduction of the portion 316 into thegroove 317. The seal 319 can constitute an O-ring, a flat annular seal,a liquid seal or a so-called flow seal. The latter can consist of asolidified flowable substance which is received in an annuar groove(shown in FIG. 6) of the casing 310. The solidified flowable substancecan include or consist of silicon rubber and/or a silicon-resin. Suchseal is disposed radially outwardly of the plenum chamber in the casing310. The latter is provided with at least one inlet for admission offlowable substance of the flow seal into the recess or groove forreception of the flow seal. The seal 431 and/or 432 a in FIG. 7 can alsoconstitute a flow seal. The flow seal or seals can be provided in one ormore recesses or grooves of the casing and/or of the guide sleeve.

At least one of the seals between the casing of the slave cylinder andthe guide sleeve can also serve to seal the conduit or conduits (such as71) which admits or admit pressurized fluid into the plenum chamber ofthe slave cylinder. The seal or seals between the casing of the slavecylinder and the guide sleeve(s) need not be round (round seals areknown in the art) but can have a maximum radius which corresponds to thesmallest radius of the guide sleeve and a minimal radius equal to orexceeding that of the conduit 71 or an equivalent thereof.

It is also possible to employ a flat annular seal which has a circularshape and the mounting and the radial dimensions of which are such thatit is coaxial with the guide sleeve; the seal and/or the casing can haveopenings which enable pressurized fluid to flow from the master cylinderinto the plenum chamber of the slave cylinder.

A flat ring-shaped seal can be provided with an axially projectingannular bead which is outwardly adjacent the guide sleeve and surroundsthe outlet of the conduit 71 (or of an equivalent or a portion, such asan adapter, of the conduit). When the guide sleeve is attached to thetransmission case, the bead is deformed and performs a reliable sealingaction.

Referring again to FIG. 7, the stop 451 can serve as an abutment for theannular piston 425 and/or for the annular clutch release bearing 451. Ifthis stop is slotted axially (see FIGS. 7 a and 7 b), it exhibitsseveral tongues (such as 452 a or 452 b) which can extend only radiallyand axially (FIG. 7 b) or radially as well as circumferentially (FIG. 7a) of the guide sleeve. Such tongues can be formed during the making ofthe guide sleeve 414, especially if the latter is made of a plasticmaterial (see FIG. 14). The stop can be an integral part of a slavecylinder housing which includes a casing 610, a guide sleeve 614 andpreferably also a fluid supplying conduit 610 a.

One or more metallic guide sleeves (reference may be had again to FIG.8) are often preferred to plastic sleeves which are of one piece withthe casing of the slave cylinder because such separately produced sleeveor sleeves contributes or contribute to stability of the slave cylinder,especially along the path for the reciprocable piston (425). Moreover,the sleeve or sleeves contributes or contribute to a reduction offriction between the internal and external surfaces of the annularpiston on the one hand, and the adjacent surfaces (428, 429) of themetallic guide sleeves on the other hand.

A presently preferred material for the separately produced guidesleeve(s) is steel as well as certain other metals (such as aluminum)and/or alloys which exhibit satisfactory characteristic regardingfrictional engagement with the piston and/or the deposition of layers orfilms which could interfere with or enhance reciprocatory movements ofthe piston in the annular chamber of the slave cylinder. It is alsopossible to make the guide sleeve(s) of a metallic material which iscapable of forming and/or retaining a particular layer or film. Suchguide sleeve(s) can be made of aluminum, magnesium and/or their alloyswhich can produce an oxide layer and contribute to desirable or optimalfrictional engagement with the piston. The oxide layer(s) can be causedto develop on purpose.

Certain other substances which can be utilized for the making ofsatisfactory guide sleeve(s) include titanium, chromium orchromium-containing metals or alloys. Still further, the guide sleeve(s)can be imparted certain desirable characteristics (especially as far asits or their frictional engagement with the piston and/or with the lipseal is concerned) by ensuring that its or their piston-contactingsurfaces are not treated (such as polished) to a high degree ofsmoothness. Thus, those portions of surfaces of the guide sleeves whichcome in contact with the reciprocable lip seal can be imparted amacrostructure which is required to accept and retain a film or layercapable of reducing the friction coefficient or establishing a desiredor desirable friction coefficient between the guide sleeve(s) and thelip seal. Such film or layer can consist of grease and/or ofmodifications of carbon (such as graphite). Suitable graphites for theapplication to the piston-contacting guide sleeve(s) are highlycondensed graphites known as glossy carbon and DL (diamond-like carbon).

Smoothness of the surfaces coming in contact with the piston and/orclutch-actuating bearing and/or lip seal can be increased to a desiredoptimum value during making of the casing of the slave cylinder. Thiscan be achieved by resorting to the aforementioned monosandwich processwhich can be resorted to in connection with the making of the casing inan injection molding machine. To this end, the machine is equipped witha discrete second extruder which admits to the primary plastic material(such as a thermoplastic or thermosetting substance) a second plasticmaterial the specific purpose of which is to impart predeterminedcharacteristics to those portions of the casing which come in contactwith the reciprocatory lip seal. The second plastic material adheres tothe exterior of that part of the casing which is made of the first orprimary plastic material but the second plastic material need not mixwith the first plastic material. The second plastic material can consistof a polymer of a fluorohydrocarbon (such as PTFE, PFA, DVDF and thelike) or of other hard plastic materials (such as PEEK, POM, PBT, PESand the like) which can be provided with a hard and smooth lipseal-contacting surface.

The plastic casing of the slave cylinder can be reinforced by fibers,such as glass fibers. The fibers need not be present in the region ofcontact with the lip seal, i.e., the aforementioned first or primaryplastic material can be reinforced by fibers but the second or secondaryplastic material (which comes in contact with the lip seal) need notcontain any fibrous reinforcing material.

The radially outer guide sleeve (such as the one shown at 430 in FIG. 8)can be provided with a radial rim which is remote from the clutchbearing 451 and abuts an adjacent surface of the, casing 410 or a partwhich is affixed to the casing. The sleeve is then held against axialmovement relative to the casing 410. A seal can be interposed betweenthe thus modified metallic sleeve 430 and the casing 410. It is alsopossible to fixedly secure the outer guide sleeve 430 to the casing 410by resorting to welding, to an adhesive or to a mechanical connectionsuch as one or more detents, snap fasteners or the like.

The connection (such as that including the conduit 71 shown in FIG. 1)between the master cylinder (70) and the plenum chamber in the plasticcasing of the slave cylinder can be selected in such a way that itsaxial length is reduced to a minimum. This can be achieved by resortingto an adapter of the type shown in FIG. 17, 18 or 19 wherein the nipple(e.g., the nipple 854) is connected to the conduit 71 and the adaptercan extend through an opening in the bell 2 c for attachment to theaxially spaced-apart casing of the slave cylinder. The adapter ensuresthat the position and/or orientation of the casing of the slave cylinderneed not conform or need not appreciably conform to the position of theopening in the bell 2 c.

The casing of the slave cylinder can be assembled of two or more partsor sections if it cannot be made of one piece due to limitations ofavailable injection molding machines, e.g., if the casing must beprovided with undercut portions which prevent the removal of such casingfrom the form or mold in an injection molding machine. Such casing canbe provided with a plug 651 of the type shown in FIG. 15, and the plugis thereupon secured to the casing (610) by resorting to an adhesive, bywelding, ultrasonic welding, by male and female threads, by caulking, bypress fitting, by snap fasteners or the like. A seal can be interposedbetween the casing and the plug.

The sensor 704 of FIG. 16 can transmit signals (via conductor means 704a) to a control circuit in the power train of the motor vehicle. Thecontrol circuit evaluates the information furnished by the conductormeans 704 a to thus ascertain the position of the piston 725. The sensor704 can constitute an inductive displacement transducer, a Hallgenerator or the like.

Friction between the piston and/or the lip seal on the one hand, and thecasing of the slave cylinder on the other hand can be reduced to ormaintained at an optimum value by resorting to the aforesaidmonosandwich undertaking or by utilizing for the casing a plasticmaterial having a least one component which contributes to a reductionof sliding friction between the piston and/or the lip seal on the onehand, and the casing of the slave cylinder on the other hand. Thecomponent can consist of or include graphite and/or apolyfluorohydrocarbon (such as PTFE). As already mentioned above, thiscomponent can constitute between about 5% and 20% (preferably betweenabout 8% and 15%) by weight of the weight of the casing of the slavecylinder. A highly satisfactory casing contains between about 35% and75% by weight of a plastic material including a thermoplastic or athermosetting substance, between about 20% and 45% of fibrousreinforcing material (such as glass fibers), and between about 5% and20% of the aforediscussed component.

Furthermore, and in order to reduce the amount of work involved in themaking and. hence the cost of the slave cylinder, as well as forecological reasons and for the convenience of assembly and dismantling(i.e., manipulation), it is normally advisable to apply special coatingsto, and to thus influence the friction between the piston and/or the lapseal on the one hand, and the plastic casing on the other hand, thoseportions of the casing or guide sleeve(s) which come into direct slidingcontact with the lip seal. The coating operation can involve theapplication of a film of nickel, chromium or the like.

A suitable method of applying films of nickel, chromium or the like caninvolve the assembly of a stack of superimposed casings with or withoutguide sleeves, to establish seals between neighboring casings to thusobtain a duct bounded by surfaces which require coating, and tothereupon apply the coating substance (such as a solution) which isrequired to complete a chemical or electrolytic coating of the surfacesby pouring the substance into the duct.

The various steps, combinations of steps, machines and/or apparatusand/or tools for carrying out the steps and/or combinations of steps andsubstances including the plastic and/or metallic substances can beutilized individually as well as in any suitable combinations inaddition to and/or in lieu of those shown in the drawing and describedhereinbefore. Furthermore, the hereinbefore described hydraulicoperating arrangement can be utilized in conjunction with a variety ofknown friction clutches, master cylinders and other constituents ofpower trains in motor vehicles. Those embodiments which are describedand claimed but not shown in full detail will be readily understood bythose adequately skilled in the art pertaining to the power trains ofmotor vehicles, and more particularly in the art pertaining to theoperating arrangements for the friction clutches of motor vehicles, uponperusal of the aforediscussed illustrated clutch operating arrangementsas well as of those shown and described in the prior art identified inthe specification of the present application.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic and specific aspects of the aboveoutlined contribution to the art of hydraulic operating arrangements forclutches and the like and, therefore, such adaptations should and areintended to be comprehended within the meaning and range of equivalenceof the appended claims.

1. A device for operating a clutch between a prime mover and achange-speed transmission in the power train of a motor vehicle,comprising: a casing including a portion confronting a part of a case ofthe transmission; and at least two substantially pin-shaped projectionsprovided on said casing and received in complementary recesses providedin said part of the transmission case, said projections havingdeformable portions extending into the respective recesses andfrictionally engaging said part of said transmission case.
 2. The deviceof claim 1, wherein said deformable portions extend radially beyond therespective projections and said openings are dimensioned to receive therespective projections with lateral play but to effect deformation ofsaid deformable portions in response to insertion of the projectionsinto the respective openings so that the deformable portions areself-lockingly retained in the respective openings.
 3. The device ofclaim 2, wherein the dimensions of said deformable portions decrease indirections as seen into the respective openings.
 4. The device of claim3, wherein said deformable portions include elastic laminations.
 5. Ahydraulically actuatable slave cylinder unit for operating a clutchbetween a prime mover and a change-speed transmission having a case anda rotary input shaft and forming part of a power train in a motorvehicle, comprising: a plastic casing; a guide sleeve provided in saidcasing and surrounding the input shaft of the transmission; an annularpiston reciprocable in an annular chamber of said casing and surroundingsaid sleeve; a clutch operating release bearing provided in said chamberand affixed to said piston; and means for securing said sleeve to atleast one of the transmission case and said casing, including a radiallyoutwardly extending flange provided at one end of said sleeve andadjacent the transmission case, said flange having a radially outerportion received in a groove of said casing, and at least one retainingmember provided in said casing and cooperating with said radially outerportion to hold said casing and said sleeve against axial movementrelative to each other.
 6. The unit of claim 5, wherein said radiallyouter portion of said flange includes an annular array of extensionsforming part of a bayonet mount of said at least one retaining member.7. The unit of claim 5, wherein said at least one retaining member is anintegral part of said casing and is deformed to overlie said radiallyouter portion subsequent to insertion of said radially outer portioninto said groove.
 8. The unit of claim 6, wherein said at least oneretaining member is deformed as a result of a treatment involving atleast one of hot caulking and ultrasonic caulking.
 9. The unit of claim5, wherein said sleeve is received in said casing in stressed condition.10. The unit of claim 9, wherein said chamber is defined by said casingjointly with said sleeve.
 11. The unit of claim 5, further comprising atleast one sealing element interposed between said casing and saidsleeve.
 12. The unit of claim 1 1, wherein said at least one sealingelement is selected from the group consisting of O-rings, flat seals,liquid seals and flow seals.
 13. The unit of claim 12, wherein said atleast one sealing element includes a flow seal having a solidifiedflowable substance received in an annular second groove of said casing.14. The unit of claim 13, wherein said solidified flowable substance isselected from the group consisting of silicon rubber and silicon resin.15. The unit of claim 13, wherein said flow seal is disposed radiallyoutwardly of said chamber and said casing has at least one inlet foradmission of said flowable substance into said second groove.
 16. Theunit of claim 15, wherein said second groove has a diameter slightlyexceeding the diameter of said chamber.
 17. The unit of claim 15,wherein said at least one sealing element includes a flow seal having aring-shaped sealing surface, said casing further having an axiallyraised sealing surface surrounding said inlet, engaged by said flow sealand in sealing engagement with said radially outer portion of saidsleeve.
 18. The unit of claim 5, further comprising a stop for one ofsaid release bearing and said piston, said stop being remote from saidflange.
 19. The unit of claim 18, wherein said stop is of one piece withsaid sleeve.
 20. The unit of claim 18, wherein said stop is arranged toprevent disengagement of said piston and said bearing from said sleevein storage and during transport of said casing.
 21. The unit of claim18, wherein said stop constitutes a deformed portion of said sleeve. 22.The unit of claim 18, wherein said stop includes at least onesubstantially radially outwardly extending tongue of said sleeve. 23.The unit of claim 18, wherein said stop includes at least one tongueforming part of and extending at least substantially circumferentiallyof said sleeve.
 24. The unit of claim 18, wherein said guide sleeveconsists at least in part of a plastic material and said stop is of onepiece with at least one of said sleeve and said casing.
 25. Ahydraulically operated disengaging system for a friction clutch in thepower train of a motor vehicle wherein the clutch is installed between aprime mover and a change-speed transmission, comprising: a mastercylinder unit; a slave cylinder unit including a casing and an annularpiston reciprocable in an annular plenum chamber of said casing; meansfor conveying pressurized hydraulic fluid from said master cylinder unitinto said plenum chamber; and an annular lip seal provided in saidchamber and slidable relative to cylindrical internal and externalsurfaces provided within said casing radially outwardly and inwardly ofsaid chamber, said casing including at least one cylindrical metallicsleeve and one of said surfaces being provided on said at least onesleeve.
 26. The system of claim 25, wherein said at least one sleeve isprovided with said external surface.
 27. The system of claim 25, whereinsaid casing comprises two cylindrical metallic sleeves one of which isprovided with said internal surface and the other of which is providedwith said external surface.
 28. The system of claim 25, wherein said atleast one sleeve consists, at least in part, of a material selected fromthe group consisting of aluminum, steel, titanium and the alloysthereof.
 29. The system of claim 25, wherein said at least one sleeveincludes a film which is provided with said at least one surface andreduces the coefficient of friction between said at least one sleeve andsaid lip seal.
 30. The system of claim 29, wherein said film containsgrease.
 31. The system of claim 29, wherein said film consists of ametal ennobling material.
 32. The system of claim 25, wherein said atleast one sleeve has a substantially radially outwardly projectingextension, said lip seal being disposed in said chamber between saidpiston and said extension and said extension having a sealing surfaceabutting a plastic portion of said casing, and further comprising asecond seal interposed between said plastic portion of said casing andsaid extension, a cover overlying said extension opposite said secondseal and means for securing said cover to said plastic portion of saidcasing.
 33. The system of claim 32, wherein said means for securing saidcover to said plastic portion of said casing includes an at leastsubstantially annular joint selected from the group consisting of weldedjoints, adhesive joints and detents.
 34. A hydraulically operateddisengaging system for a friction clutch in the power train of a motorvehicle wherein the clutch is installed between a prime mover and achange-speed transmission, comprising: a master cylinder unit; a slavecylinder unit including a casing and an annular piston reciprocable inan annular plenum chamber of said casing, said casing consisting atleast in part of a plastic material; means for conveying pressurizedhydraulic fluid from said master cylinder unit into said plenum chamber;and at least one sensor associated with said casing and arranged tomonitor the positions of said piston in said chamber.
 35. The system ofclaim 34, wherein said at least one sensor is arranged to monitordistances covered by said piston in said chamber.
 36. The system ofclaim 34, wherein said at least one sensor is at least partiallyembedded in said casing.
 37. The system of claim 36, wherein casing isan injection molded article.
 38. The system of claim 36, wherein saidmeans for conveying includes a tubular extension of said casing andfurther comprising conductor means embedded in said extension andconnected with said at least one sensor.
 39. A hydraulically operateddisengaging system for a friction cutch in the power train of a motorvehicle wherein the clutch is installed between a prime mover and achange-speed transmission, comprising: a master cylinder unit; a slavecylinder unit including a casing having an annular plenum chamber, anannular piston reciprocable in said chamber, a first cylindrical surfacesurrounding said chamber, a second cylindrical surface surrounded bysaid chamber, an annular lip seal disposed in said chamber, sealinglyengaging said surfaces and reciprocable with said piston along and insealing engagement with predetermined portions of said surfaces, and ametallic film provided at least on said predetermined portion of atleast one of said surfaces; and means for conveying pressurizedhydraulic fluid from said master cylinder into said plenum chamber. 40.A hydraulically operated disengaging system for a friction clutch in thepower train of a motor vehicle wherein the clutch is arranged to operatebetween a prime mover and a change-speed transmission, comprising: amaster cylinder; a slave cylinder including a casing, a metallic sleevereceived in said casing, defining with said casing an annular chamberand having limited freedom of radial movement relative to said chamber,an annular piston reciprocably received in said chamber, and an annularlip seal reciprocable in said chamber with said piston and having aninternal surface sealingly engaging said sleeve and an external surfacesealingly engaging said casing; and means for conveying pressurizedhydraulic fluid from said master cylinder into said chamber.